Level shifter and related methods and apparatus

ABSTRACT

Apparatus and methods are provided directed to a device, including at least one ultrasonic transducer, a level shifter coupled to the at least one ultrasonic transducer, the level shifter including an input terminal configured to receive an input voltage, an output terminal configured to provide an output voltage level-shifted from the input voltage, a capacitor coupled between the input terminal and the output terminal, and a diode coupled in reverse-biased configuration between an input to an active high voltage element and a first voltage of a high voltage power supply.

BACKGROUND

1. Field

The present application relates to ultrasound devices having a multi-level pulser and/or a level shifter.

2. Related Art

Ultrasound devices may be used to perform diagnostic imaging and/or treatment. Ultrasound imaging may be used to see internal soft tissue body structures. Ultrasound imaging may be used to find a source of a disease or to exclude any pathology. Ultrasound devices use sound waves with frequencies which are higher than those audible to humans. Ultrasonic images are made by sending pulses of ultrasound into tissue using a probe. The sound waves are reflected off the tissue, with different tissues reflecting varying degrees of sound. These reflected sound waves may be recorded and displayed as an image to the operator. The strength (amplitude) of the sound signal and the time it takes for the wave to travel through the body provide information used to produce an image.

Many different types of images can be formed using ultrasound devices. The images can be real-time images. For example, images can be generated that show two-dimensional cross-sections of tissue, blood flow, motion of tissue over time, the location of blood, the presence of specific molecules, the stiffness of tissue, or the anatomy of a three-dimensional region.

SUMMARY

According to aspects of the present application, there are provided apparatus and methods directed to an apparatus, including at least one ultrasonic transducer, a level shifter coupled to the at least one ultrasonic transducer, the level shifter including an input terminal configured to receive an input voltage, an output terminal configured to provide an output voltage level-shifted from the input voltage, a capacitor coupled between the input terminal and the output terminal, and a diode coupled in reverse-biased configuration between an input to an active high voltage element and a first voltage of a high voltage power supply.

According to aspects of the present application, there are provided apparatus and methods directed to a level shifter, including an input terminal configured to receive an input voltage, an output terminal configured to provide an output voltage level-shifted from the input voltage, a capacitor coupled between the input terminal and the output terminal, and a diode coupled in reverse-biased configuration between an input to an active high voltage element and a first voltage of a high voltage power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and embodiments of the application will be described with reference to the following figures. It should be appreciated that the figures are not necessarily drawn to scale. Items appearing in multiple figures are indicated by the same reference number in all the figures in which they appear.

FIG. 1 is a block diagram of an ultrasound device including a multi-level pulser and a level shifter, according to a non-limiting embodiment of the present application.

FIG. 2 illustrates a non-limiting circuit diagram of a multi-level pulser, according to a non-limiting embodiment of the present application.

FIG. 3A illustrates a circuit diagram of a first embodiment of a level shifter, according to a non-limiting embodiment of the present application.

FIG. 3B illustrates a circuit diagram of a second embodiment of a level shifter, according to a non-limiting embodiment of the present application.

FIG. 4A illustrates a non-limiting equivalent circuit of the circuit of FIG. 2, during a first phase of a multi-level pulse formation, according to a non-limiting embodiment of the present application.

FIG. 4B illustrates a non-limiting equivalent circuit of the circuit of FIG. 2, during a second phase of a multi-level pulse formation, according to a non-limiting embodiment of the present application.

FIG. 4C illustrates a non-limiting equivalent circuit of the circuit of FIG. 2, during a third phase of a multi-level pulse formation, according to a non-limiting embodiment of the present application.

FIG. 4D illustrates a non-limiting equivalent circuit of the circuit of FIG. 2, during a fourth phase of a multi-level pulse formation, according to a non-limiting embodiment of the present application.

FIG. 4E illustrates a non-limiting equivalent circuit of the circuit of FIG. 2, during a fifth phase of a multi-level pulse formation, according to a non-limiting embodiment of the present application.

FIG. 4F illustrates a non-limiting equivalent circuit of the circuit of FIG. 2, during a sixth phase of a multi-level pulse formation, according to a non-limiting embodiment of the present application.

FIG. 5 is a graph illustrating a non-limiting example of a time-dependent multi-level pulse and the control signals, according to a non-limiting embodiment of the present application.

DETAILED DESCRIPTION

The inventors have recognized and appreciated that the power necessary to transmit high-intensity pulses may be greatly decreased by forming electric pulses having multiple levels.

Aspects of the present application relate to high-intensity focused ultrasound (HIFU) procedures that may be used to focus high-intensity ultrasound energy on targets to treat diseases or damaged tissues by selectively increasing the temperature of the target or the region surrounding the target. HIFU procedures may be used for therapeutic or ablative purposes. Pulsed signals may be used to generate HIFUs. According to aspects of the present application, the generation of such high-intensity pulses may require driving voltages of several tens to several hundreds of volts.

The power consumption associated with the generation of typical 2-level pulses having a “low” voltage and a “high” voltage is proportional to the square of the high voltage. For example, the generation of a 2-level pulse having a “low” voltage equal to 0 requires a power equal to: P ₍₂₎ =C*V ² *f where P₍₂₎ is the power needed to generate the 2-level pulse, C is the capacitance of the load receiving the pulse, V is the “high” voltage and f is the repetition frequency of the 2-level pulse.

According to aspects of the present application, the power consumption associated with the generation of pulses for HIFU procedures may exceed several tens to thousands of watts, thus causing the circuit to generate significant amounts of heat.

Aspects of the present application relate to multi-level pulsers designed to decrease power consumption and heat dissipation.

Furthermore, aspects of the present application relate to a level shifter circuit configured to drive the multi-level pulser. The level shifter disclosed herein may dissipate considerably less power compared to typical level shifters. Accordingly, power may be dissipated only when a level is switched, while static power consumption may be negligible.

The aspects and embodiments described above, as well as additional aspects and embodiments, are described further below. These aspects and/or embodiments may be used individually, all together, or in any combination of two or more, as the application is not limited in this respect.

FIG. 1 illustrates a circuit for processing received ultrasound signals, according to a non-limiting embodiment of the present application. The circuit 100 includes N ultrasonic transducers 102 a . . . 102 n, wherein N is an integer. The ultrasonic transducers are sensors in some embodiments, producing electrical signals representing received ultrasound signals. The ultrasonic transducers may also transmit ultrasound signals in some embodiments. The ultrasonic transducers may be capacitive micromachined ultrasonic transducers (CMUTs) in some embodiments. The ultrasonic transducers may be piezoelectric micromachined ultrasonic transducers (PMUTs) in some embodiments. Further alternative types of ultrasonic transducers may be used in other embodiments.

The circuit 100 further comprises N circuitry channels 104 a . . . 104 n. The circuitry channels may correspond to a respective ultrasonic transducer 102 a . . . 102 n. For example, there may be eight ultrasonic transducers 102 a . . . 102 n and eight corresponding circuitry channels 104 a . . . 104 n. In some embodiments, the number of ultrasonic transducers 102 a . . . 102 n may be greater than the number of circuitry channels.

According to aspects of the present application, the circuitry channels 104 a . . . 104 n may include transmit circuitry. The transmit circuitry may include level shifters 106 a . . . 106 n coupled to respective multi-level pulsers 108 a . . . 108 n. The multi-level pulsers 108 a . . . 108 n may control the respective ultrasonic transducers 102 a . . . 102 n to emit ultrasound signals.

Circuitry channels 104 a . . . 104 n may also include receive circuitry. The receive circuitry of the circuitry channels 104 a . . . 104 n may receive the electrical signals output from respective ultrasonic transducers 102 a . . . 102 n. In the illustrated example, each circuitry channel 104 a . . . 104 n includes a respective receive switch 110 a . . . 110 n and an amplifier 112 a . . . 112 n. The receive switches 110 a . . . 110 n may be controlled to activate/deactivate readout of an electrical signal from a given ultrasonic transducer 102 a . . . 102 n. More generally, the receive switches 110 a . . . 110 n may be receive circuits, since alternatives to a switch may be employed to perform the same function. The amplifiers 112 a . . . 112 n may be trans-impedance amplifiers (TIAs).

The circuit 100 further comprises an averaging circuit 114, which is also referred to herein as a summer or a summing amplifier. In some embodiments, the averaging circuit 114 is a buffer or an amplifier. The averaging circuit 114 may receive output signals from one or more of the amplifiers 112 a . . . 112 n and may provide an averaged output signal. The averaged output signal may be formed in part by adding or subtracting the signals from the various amplifiers 112 a . . . 112 n. The averaging circuit 114 may include a variable feedback resistance. The value of the variable feedback resistance may be adjusted dynamically based upon the number of amplifiers 112 a . . . 112 n from which the averaging circuit receives signals. The averaging circuit 114 is coupled to an auto-zero block 116.

The auto-zero block 116 is coupled to a time gain compensation circuit 118 which includes an attenuator 120 and a fixed gain amplifier 122. Time gain compensation circuit 118 is coupled to an analog-to-digital converter (ADC) 126 via ADC drivers 124. In the illustrated example, the ADC drivers 124 include a first ADC driver 125 a and a second ADC driver 125 b. The ADC 126 digitizes the signal(s) from the averaging circuit 114.

While FIG. 1 illustrates a number of components as part of a circuit of an ultrasound device, it should be appreciated that the various aspects described herein are not limited to the exact components or configuration of components illustrated. For example, aspects of the present application relate to the multi-level pulsers 108 a . . . 108 n and the level shifters 106 a . . . 106 n.

The components of FIG. 1 may be located on a single substrate or on different substrates. For example, as illustrated, the ultrasonic transducers 102 a . . . 102 n may be on a first substrate 128 a and the remaining illustrated components may be on a second substrate 128 b. The first and/or second substrates may be semiconductor substrates, such as silicon substrates. In an alternative embodiment, the components of FIG. 1 may be on a single substrate. For example, the ultrasonic transducers 102 a . . . 102 n and the illustrated circuitry may be monolithically integrated on the same semiconductor die. Such integration may be facilitated by using CMUTs as the ultrasonic transducers.

According to an embodiment, the components of FIG. 1 form part of an ultrasound probe. The ultrasound probe may be handheld. In some embodiments, the components of FIG. 1 form part of an ultrasound patch configured to be worn by a patient.

FIG. 2 illustrates the circuit diagram of a multi-level pulser, according to aspects to the present application. In some embodiments, multi-level pulser 200 may be configured to transmit a pulse to capacitor C. Capacitor C may represent the capacitance associated with an ultrasound transducer. For example, capacitor C may represent a capacitive micromachined ultrasonic transducer (CMUT). However, multi-level pulser 200 may be configured to transmit a pulse to a resistor, a resistive network or a network exhibiting any suitable combination of resistive and reactive elements.

In the non-limiting embodiment illustrated in FIG. 2, multi-level pulser 200 is configured to provide an N-level pulse, where N may assume any value greater than 2. The power consumption P_((N)) associated with the transmission of a N-level pulser to capacitor C is equal to: P _((N)) =C*V ² *f/(N−1) where f is the repetition frequency of the pulsed waveform. Accordingly, power consumption is reduced by a factor N−1 compared to typical 2-level pulsers.

In some embodiments, N-level pulser 200 may comprise 2N−2 transistors and 2N−4 diodes. However, any suitable number of transistors may be used. Among the 2N−2 transistors, N−1 may exhibit one type of conductivity and N−1 may exhibit the opposite type of conductivity. However any other suitable combination of types of conductivity may be used. For example, N−1 transistors may be nMOS and N−1 transistors may be pMOS. However any other suitable type of transistor may be used.

N-level pulser 200 may comprise N circuit blocks 201 ₁, 201 ₂ . . . 201 _(N). The N circuit blocks may be connected to node 202. One terminal of capacitor C may also be connected to node 202. The second terminal of capacitor C may be connected to ground. Circuit block 201 ₁ may comprise pMOS transistor T₁, having the source connected to a reference voltage V_(DD) and the drain connected to node 202. Reference voltage V_(DD) may be a voltage supply. The gate of transistor T₁ may be driven by signal V_(G1).

Circuit block 201 _(N) may comprise nMOS transistor T_(2N-2), having the source connected to a reference voltage V_(SS) and the drain connected to node 202. In some embodiments, reference voltage V_(SS) may be less than reference voltage V_(DD). However, pulser 200 is not limited in this respect. Furthermore, reference voltage V_(SS) may positive, negative or equal to zero. The gate of transistor T_(2N-2) may be driven by signal V_(G2N-2).

In some embodiments, circuit blocks 201 ₂ may comprise two transistors T₂ and T₃ and two diodes D₂ and D₃. Transistor T₂ and diode D₂ may be connected in series and transistor T₃ and diode D₃ may also be connected in series. The two series may be connected in parallel. In some embodiments, T₂ may be a pMOS transistor, having the source connected to the reference voltage V_(MID2) and the drain connected to the anode of D₂ and T₃ may be an nMOS transistor, having the source connected to V_(MID2) and the drain connected to the cathode of D₃. In some embodiments, V_(MID2) may be greater than V_(SS) and less than V_(DD). The cathode of D₂ and the anode of D₃ may be connected to node 202. Furthermore, the gate of T₂ may be driven by signal V_(G2) and the gate of T₃ may be driven by signal V_(G3).

In some embodiments, circuit blocks 201 ₁, where i may assume any value between 3 and N−1, may comprise two transistors T_(2i-2) and T_(2i-1) and two diodes D_(2i-2) and D_(2i-1). Transistor T_(2i-2) and diode D_(2i-2) may be connected in series and transistor T₂₋₁ and diode D_(2i-1) may also be connected in series. The two series may be connected in parallel. In some embodiments, T_(2i-2) may be a pMOS transistor, having the source connected to the reference voltage V_(MIDi) and the drain connected to the anode of D_(2i-2) and T_(2i-1) may be an nMOS transistor, having the source connected to V_(MID) and the drain connected to the cathode of D_(2i-1). In some anode of D_(2i-4) may be connected to node 202. Furthermore, the gate of T_(2i-2) may be driven by signal V_(G2i-2) and the gate of T_(2i-1) may be driven by signal V_(G2i-1).

V_(DD), V_(SS) and V_(MIDi), for any value of i, may have values between approximately −300V and 300V, between approximately −200V and 200V, or any suitable value or range of values. Other values are also possible.

FIG. 3A and FIG. 3B illustrate two non-limiting embodiments of a level shifter circuit, according to aspects of the present application. In some embodiments, level shifter 301, shown in FIG. 3A, may be integrated on the same chip as pulser 200. In some embodiments, level shifter 301 may be used to drive any of the pMOS transistors of pulser 200. For example, level shifter 301 may be used to output signal V_(G2i-2) to drive the gate of transistor T_(2i-2). The input voltage V_(IN2i-2) to level shifter 301 may be a control signal having two possible voltage levels: V_(SS) and V_(SS)+δV, where δV may assume any suitable value or range of values. In some embodiments, control signal V_(IN2i-2) may be generated by a circuit integrated on the same chip as level shifter 301. However, control signal V_(IN2i-2) may also be generated by a circuit integrated on a separate chip. In some embodiments, level shifter 301 may comprise an inverter I_(M1), followed by capacitor C_(M). The power supply pins of inverter I_(M1) may be connected to voltages V_(SS) and V_(SS)+δV. Capacitor C_(M) may be followed by the series of a number of inverters. In some embodiments, capacitor C_(M) is followed by three inverters I_(M2), I_(M3) and I_(M4). The “−” and “+” power supply pins of inverter I_(M2), I_(M3) and I_(M4) may be connected to voltages V_(MIDi)−ΔV and V_(MIDi) respectively. In some non-limiting embodiments, level shifter 301 may comprise diode D_(M). The cathode or diode D_(M) may be connected to the output of capacitor C_(M), while the anode may be connected to the V_(MIDi)−ΔV rail. While level shifter 301 comprises four inverters in the non-limiting embodiment of FIG. 3A, any suitable number of inverters may otherwise be used. Output voltage V_(G2i-2) may assume two possible voltages: V_(MIDi)−ΔV and V_(MIDi).

In some embodiments, level shifter 302, shown in FIG. 3B, may be integrated on the same chip as pulser 200. In some embodiments, level shifter 302 may be used to drive any of the nMOS transistors of pulser 200. For example, level shifter 302 may be used to output signal V_(G2i-1) to drive the gate of transistor T_(2i-1). The input voltage V_(IN2i-1) to level shifter 302 may be a control signal having two possible voltage levels: V_(SS) and V_(SS)+δV. In some embodiments, control signal V_(IN2i-1) may be generated by a circuit integrated on the same chip as level shifter 302. However, control signal V_(IN2i-1) may also be generated by a circuit integrated on a separate chip. In some embodiments, level shifter 302 may comprise an inverter I_(P1), followed by capacitor C_(P). The power supply pins of inverter I_(P1) may be connected to voltages V_(SS) and V_(SS)+δV. Capacitor C_(P) may be followed by the series of a number of inverters. In some embodiments, capacitor C_(P) is followed by two inverters I_(P2) and I_(P3). The power supply pins of inverter I_(M2) and I_(M3) may be connected to voltages V_(MIDi) and V_(MIDi)+ΔV. In some non-limiting embodiments, level shifter 302 may comprise diode DP. The cathode or diode D_(P) may be connected to the output of capacitor C_(P), while the anode may be connected to the V_(MIDi) rail. While level shifter 302 comprises three inverters in the non-limiting embodiment of FIG. 3B, any suitable number of inverters may otherwise be used. Output voltage V_(G2i-i) may assume two possible voltages: V_(MIDi) and V_(MIDi)+ΔV.

According to aspects of the present application, level shifters 301 and 302 may dissipate power only when a level is switched, while static power may be negligible. Capacitors C_(M) and C_(P) may be used to shift the voltage level by storing a constant voltage drop across them. For example, the static power consumption may be less than 100 mW, less than 1 mW, less than 1 μW or less than any suitable value.

FIG. 4A, FIG. 4B, FIG. 4C, FIG. 4D, FIG. 4E, and FIG. 4F illustrate six snapshots of pulser 200 corresponding to the six phases associated with the formation of a 4-level pulse, according to aspects on the present application. In the figures, only the active blocks are shown. While in the non-limiting example N is equal to 4, any other suitable value of N, such that N is greater than 2, may otherwise be used. In the example, V_(SS) is set to 0.

FIG. 5 illustrates a non-limiting example of multi-level pulse 500 generated according to aspects of the present application. In the non-limiting example, pulse 500 exhibits 4 levels: 0, V_(MID3), V_(MID2), and V_(DD). In addition, FIG. 5 illustrates the 6 control signals V_(G1), V_(G2), V_(G3), V_(G4), V_(G5), and V_(G6) used to respectively drive the gates of transistors T₁, T₂, T₃, T₄, T₅, and T₆. The process associated with the pulse generation can be divided in 6 phases. Between t₁ and t₂, pulse 500 may be increased from 0 to V_(MID3) by providing a negative pulse 504 to transistor T₄ through V_(G4) as shown in FIG. 5. FIG. 4A illustrates pulser 201 between t₁ and t₂. During this period, the gate of transistor T₄ may be driven by a voltage equal to V_(MID3)−ΔV. ΔV may be chosen so as to create a conductive channel and cause transistor T₄ to drive a current between the source and the drain passing through diode D₄. Such current may charge capacitor C, such that an output voltage of V_(MID3) is obtained, neglecting any voltage drop on T₄ and D₄. Pulse 504 may be obtained through level shifter 301.

Between t₂ and t₃, pulse 500 may be increased from V_(MID3) to V_(MID2) by providing a negative pulse 502 to transistor T₂ through V_(G2) as shown in FIG. 5. FIG. 4B illustrates pulser 201 between t₂ and t₃. During this period, the gate of transistor T₂ may be driven by a voltage equal to V_(MID2)−ΔV. ΔV may be chosen so as to create a conductive channel and cause transistor T₂ to drive a current between the source and the drain passing through diode D₂. Such current may charge capacitor C, such that an output voltage of V_(MID2) is obtained, neglecting any voltage drop on T₂ and D₂. Pulse 502 may be obtained through level shifter 301.

Between t₃ and t₄, pulse 500 may be increased from V_(MID2) to V_(DD) by providing a negative pulse 501 to transistor T₁ through V_(G1) as shown in FIG. 5. FIG. 4C illustrates pulser 201 between t₃ and t₄. During this period, the gate of transistor T₁ may be driven by a voltage equal to V_(DD)−ΔV. ΔV may be chosen so as to create a conductive channel and cause transistor T₁ to drive a current between the source and the drain. Such current may charge capacitor C, such that an output voltage of V_(DD) is obtained, neglecting any voltage drop on T₁. Pulse 501 may be obtained through level shifter 301.

Between t₄ and t₅, pulse 500 may be decreased from V_(DD) to V_(MID2) by providing a positive pulse 503 to transistor T₃ through V_(G3) as shown in FIG. 5. FIG. 4D illustrates pulser 201 between t₄ and t₅. During this period, the gate of transistor T₃ may be driven by a voltage equal to V_(MID2)+ΔV. ΔV may be chosen so as to create a conductive channel and cause transistor T₃ to drive a current between the drain and the source. Such current may discharge capacitor C, such that an output voltage of V_(MID2) is obtained, neglecting any voltage drop on T₃ and D₃. Pulse 503 may be obtained through level shifter 302.

Between t₅ and t₆, pulse 500 may be decreased from V_(MID2) to V_(MID3) by providing a positive pulse 505 to transistor T₅ through V_(G5) as shown in FIG. 5. FIG. 4E illustrates pulser 201 between t₅ and t₆. During this period, the gate of transistor T₅ may be driven by a voltage equal to V_(MID3)+ΔV. ΔV may be chosen so as to create a conductive channel and cause transistor T₅ to drive a current between the drain and the source. Such current may discharge capacitor C, such that an output voltage of V_(MID3) is obtained, neglecting any voltage drop on T₅ and D₅. Pulse 505 may be obtained through level shifter 302.

After t₆, pulse 500 may be decreased from V_(MID3) to 0 by providing a positive pulse 506 to transistor T₆ through V_(G6) as shown in FIG. 5. FIG. 4F illustrates pulser 201 after t₆. During this period, the gate of transistor T₆ may be driven by a voltage equal to ΔV. ΔV may be chosen so as to create a conductive channel and cause transistor T₆ to drive a current between the drain and the source. Such current may discharge capacitor C, such that an output voltage of 0 is obtained, neglecting any voltage drop on T₆. Pulse 506 may be obtained through level shifter 302.

In the non-limiting example in connection to FIG. 5, pulse 500 is unipolar. However, multi-level pulser 200 in not limited in this respect. Multi-level pulser 200 may alternatively be configured to transmit bipolar pulses exhibiting levels having positive and negative voltages. In accordance with another aspect of the present application, the multi-level pulser 200 may be considered a multi-level charge recycling waveform generator in that charge recycling occurs on the decrementing step as charge is transferred from the output capacitance back into the power supply. In accordance with another aspect of the present application, although the multi-level pulser has been described as being used to drive a capacitive output, it may also be used to drive a resistive output.

The amount of power saving when using a level shifter of the types described herein may be significant. In some embodiments, utilizing a level shifter of the type described herein may provide substantial power saving by setting the static power consumption to approximately zero. Accordingly, power may be dissipated only during switching states.

Having thus described several aspects and embodiments of the technology of this application, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those of ordinary skill in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described in the application. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described.

As described, some aspects may be embodied as one or more methods. The acts performed as part of the method(s) may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases.

As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements.

As used herein, the term “between” used in a numerical context is to be inclusive unless indicated otherwise. For example, “between A and B” includes A and B unless indicated otherwise.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively. 

What is claimed is:
 1. An apparatus, comprising: at least one ultrasonic transducer on a substrate, and a level shifter on the substrate coupled to the at least one ultrasonic transducer, the level shifter including an input terminal configured to receive an input voltage; an output terminal configured to provide an output voltage level-shifted from the input voltage; a capacitor coupled between the input terminal and the output terminal; and a diode coupled in reverse-biased configuration between an input to an active high voltage element and a first voltage of a high voltage power supply; wherein the input of the active high voltage element is coupled to an output of the capacitor.
 2. The apparatus of claim 1, wherein the active high voltage element comprises an inverter.
 3. The apparatus of claim 1, wherein the high voltage power supply has two voltages, and wherein the first voltage is one of the two voltages.
 4. A level shifter, comprising: an input terminal configured to receive an input voltage; an output terminal configured to provide an output voltage level-shifted from the input voltage; a capacitor coupled between the input terminal and the output terminal; and a diode coupled in reverse-biased configuration between an input to an active high voltage element and a first voltage of a high voltage power supply; wherein the input of the active high voltage element is coupled to an output of the capacitor.
 5. The level shifter of claim 4, wherein the active high voltage element comprises an inverter.
 6. The level shifter of claim 4, wherein the high voltage power supply has two voltages, and wherein the first voltage is one of the two voltages. 